1. Field of the Invention
This invention relates to switching regulars, and more particularly, to a pulse-width controller for use in a switching regulator for pulse width modulation of a square-wave signal used to control the output of the switching regulator.
2. Description of Related Art
FIG. 1 is a schematic circuit diagram of a conventional switching regulator. As shown, this switching regulator includes a controller 100a and a bulk regulator 100b. The controller 100a is composed of an amplifier 10a, a comparator 10b, and an oscillator 10c. The oscillator 10c is used to generate a triangle-wave signal. The output power of the switching regulator is dependent on the duty cycle of a square-wave signal generated by the controller 100a, and this-square-wave signal is applied to a switching transistor Q.sub.1 in the bulk regulator 100b. The output power of the bulk regulator 100b is proportional to the pulse width of this square-wave signal. To provide feedback control of the square-wave signal, the output voltage V.sub.O of the bulk regulator 100b is divided by a pair of resistors R.sub.1, R.sub.2 to obtained an apportioned feedback voltage V.sub.feedback which is then fed back to the amplifier 10a. The amplifier 10a takes both V.sub.feedback and a reference voltage V.sub.ref as inputs so as to amplify the difference between these two signals. The output of the amplifier 10a is compared by the comparator 10b with the triangle-wave output of the oscillator 10c to thereby generate a square-wave signal to control the switching transistor Q.sub.1. When the output voltage V.sub.O falls below the desired level, the fall will be indicated by a drop in V.sub.feedback that then causes the controller 100a to increase the duty cycle of the square-wave output of the comparator 10b, thereby increasing the level of the output voltage V.sub.O until it reaches the desired level. On the other hand, when the output voltage V.sub.O rises above the desired level, the rise in V.sub.feedback can cause the controller 100a to decrease the duty cycle of the square-wave output of the comparator 10b, thereby decreasing the level of the output voltage V.sub.O until it reaches the desired level. This allows the switching regulator to output a fixed output voltage V.sub.O. The fixed level of the output voltage V.sub.O can be adjusted by varying the ratio R.sub.2 /R.sub.1 and the reference voltage V.sub.ref.
One drawback to the foregoing switching regulator, however, is that its dynamic characteristics are not quite satisfactory since it has output voltage feedback only and no output current feedback.
FIG. 2 is a schematic circuit diagram of another conventional switching regulator As shown, this switching regulator differs from the one of FIG. 1 in that this switching regulator further includes two feedback networks 20a, 20b. The first feedback network 20a connects the output end of the amplifier 10a back to one input end of the same; while the second feedback network 20b connects the output voltage V.sub.O back to one input end of the amplifier 10a and also via the first feedback network 20a to one input end of the comparator 10b that is connected to the output of the amplifier 10a. These two feedback networks 20a, 20b are both configured with resistors and capacitors. These capacitors are large in capacitance that can allow an increase in the gain bandwidth of the switching regulator.
One drawback to the foregoing switching regulator, however, is that, since the feedback networks 20a, 20b include large-capacitance capacitors to build, the integrated circuit implementing the switching regulator will take up large space in circuit layout area. This drawback will reduce the cost-effectiveness in the manufacture of the switching regulator.